The present invention relates generally to semiconductor electrical fuse devices, and more particularly to the protection of electrical fuses from accidental programming and electric static discharge (ESD).
Demands are escalating for sub-micron semiconductor devices with high density, high reliability, and large-scale integration. These semiconductor devices require increased transistor and circuit performance, high reliability and increased manufacturing throughput.
Traditionally, integrated circuits containing these semiconductor devices include laser fuses, which are used to provide repairs to the circuit. These laser fuses are programmed by firing a low-power, extremely focused laser thereto, thereby melting the fuse and “blowing” it apart. Melted fuses are then used to repair one or more parts of an integrated circuit. As an example, lasers fuses are normally used during the testing portion of the manufacturing process before each individual integrated circuit is cut from a semiconductor wafer. Most integrated circuits have built-in test engines that detect any faults incurred during the manufacturing process, and share that information with an outside technician who
While this method is effective, it is also tedious, time consuming, and prone to an operator's error. In addition, because laser fuses are also large in physical size, they typically use up too much space in a wafer. In modern day sub-micron designs, the large sizes of these laser fuses become an issue.
Another method to repair integrated circuits is to use electrical fuses. Electrical fuses are preferred to laser fuses because they can be placed anywhere under the metal structure of a chip, thus potentially allowing for thousands of fuses to be used in a single chip. Electrical fuses are designed to break when a large electrical current passes through them. By “blowing” these fuses during testing, technicians can monitor and adjust their functions to improve their quality, performance and power consumption without much human intervention.
However, there is currently no effective method to protect electrical fuses from false programming. Because the physical structure of an electrical fuse is very small and fragile, a typical resistance would range around 100 ohms, and devices with such small resistance are sensitive to electrical static discharge (ESD) and floating supply voltage that can reside inside an integrated circuit containing them. Both ESD and floating supply voltage can potentially cause these electrical fuses to accidentally program themselves while in the manufacturing stage or during physical contact in a human body model. Therefore, it is desirable in the art of electrical fuse designs to provide improved build-in protection, thereby increasing reliability and production yield.